1. Field of the Invention
The present invention relates to a lens barrel having plural optical systems that are movable in a common optical axis direction.
2. Description of the Related Art
Conventionally, a lens barrel having plural optical systems movable in a common optical axis direction has been known. For example, there are image pickup apparatuses (such as a silver halide camera, digital camera, and digital video camera) having a zoom lens barrel that is movable between a storage position and a photographing position in an optical direction to change photographing magnification.
Such a conventional zoom lens barrel is generally provided with a photointerrupter (PI sensor) fixed to a stationary frame of the lens barrel and serving as a reset sensor for detecting whether a lens holding frame is moved up to a reset position. The lens holding frame is mounted with a light shield plate for intercepting light directed toward the PI sensor. Whether a light receiving device of the IP sensor is in a light-shielded state or in a non-light-shielded state is determined to thereby detect, as the reset position of the lens holding frame, a position of changeover between the light-shielded state and the non-light-shielded state.
Japanese Patent Publication No. 2856557 discloses an image pickup apparatus that detects relative positions of first and second group lens units of a lens barrel. In this image pickup apparatus, a photodetector (corresponding to the photointerrupter) is fixed to the second group lens unit and a slit plate (corresponding to the light shield plate) is mounted to a lens holding frame which is movable and holds the first group lens.
However, since the conventional image pickup apparatus requires that a place for installation of the photointerrupter be provided in the stationary frame, the degree of freedom of installation of the photointerrupter becomes low and the lens barrel becomes large in size. If an attempt is made to freely set the position of changeover between light-shielded state and non-light-shielded state, the light shield plate becomes long. This poses a problem that a detection mechanism including the photointerrupter becomes large. In particular, the image pickup apparatus disclosed in Japanese Patent Publication No. 2856557 requires a space for installation of a large slit plate, posing a problem that the lens barrel becomes large in size.